Interference eliminating device



March 16, 1937. W. M. RoBlNsoN 2,073,880

INTERFERENCE EL IMINATING DEVICE Filed June 19, 1935 ATTORNEY Patented Mar. 16, 1937 UNITED STATES dass PATENT GFFIQE INTERFERENCE ELIMINATING DEVICE Application June 19,

6 Claims.

This invention concerns an appliance adapted to be used in radio receiving circuits and its general purpose is to eliminate interference and other extraneous disturbances.

Among such appliances may be counted induction coils used for different technical or medical purposes, Y-ray apparatus, Tesla transformers, ultra-violet ray lamps, electric vacuum cleaners, fiat irons and cookers, etc. But while interference, due to natural, i. e. atmospheric sources, is mostly, if not exclusively, picked up by the receiving antenna, the second class of disturbances is often directly transmitted to the receiving radio circuit over the service power line into which the so-called electrified receiving set is plugged whether the electric appliances causing interference are on the same line or near by.

The usual means, employed to eliminate interference consists in connecting a condenser of suitable capacity or across the power line leadins. A similar effect, eliminating radio interference, can be attained by shunting such condenser at the source of the interfering disturbance, i. e. across the power lines, actuating the electrical appliance or tool. These same well known principles are used also in this invention and no claim is laid regarding the discovery or specic use of said principles per se; the alleged novelty is rather the specic form or construction in which this principle is embodied.

More accurately expressed:

The first object of my invention is to provide an eliminator lfor radio noises of man-made origin.

Another object of the invention is to provide an eliminator for the purpose described and adapted to be used in rado-receiving sets, actuated from service power lines, e. g. the usual A. C. or D. C. house current.

A further object of my invention is to provide an interference eliminator that can be readily attached over the terminal prongs of the standard plug by means of which the receiving set or the electrical device producing interference is plugged into any standard socket of an A. C. or D. C. service line.

Another object is to provide an interference eliminator of the kind described of much simplified construction, compared with other similar previous devices.

A further corollary object is to devise such an appliance which may consist oi fewer parts and can consequently be manufactured at a lower cost.

A concurrent object is to provide an interfer- 1935, Serial No. 27,341

(Cl. Z50-16) ence eliminator of man-made radio noises which is simple, compact and of very small dimensions, so that, when installed, it will be inconspicuous.

A further object of my invention is to devise an eliminator for the purpose described which has only two positive contacts instead of four, which previous similar devices show.

Other objects will become apparent from the following specication and the drawing which illustrates an embodiment of the present inventive conception, but it is to be understood that the same is only illustrative and not restrictive and that other modifications are possible without deviating from the principle of the invention. Similar reference numerals denote similar parts throughout the different views.

Fig. 1 is a front elevation of an interference eliminator built according to the principles of my invention and shown at a somewhat enlarged scale.

Fig. 2 is a side elevation of the eliminator and indicates in dot and dash lines how the prongs of a standard plug are inserted through the slots of the eliminator into a wall socket.

Fig. 3 shows the inner construction of the eliminator. The protective ferrule of the condenser and the insulating front panel with the eyelets have been removed.

Fig. 4 shows at a greatly exaggerated scale a longitudinal cross section through the eliminator, taken along the line 4 4 of Fig. 1 or Fig. 3.

Fig. 5 shows, about in actual size, the intermediate non-conductive plate, supporting the two terminal clamps of the Xed condenser, seated upon the prongs.

Fig. 6 shows in actual size one of the aforesaid terminal clamps.

Referring mode in detail to the different views, the essential operative element of the device is a xed paper-wound condenser lil, shown in elevation in Fig. 3 and in section in Fig. 4. The construction of such condensers is well known. They consist essentially of a pair of spirally wound metal foil strips, insulated from each other by parafined paper or a similar non-conducting layer, each foil strip connected to a separate terminal wire lla and IIb respectively.

The spiral lm roll is encased in a non-conducting tube Hla and the open ends are usually hermetically sealed around the terminal wires by wax, asphalt or a similar material. Each terminal wire is with its end soldered to a clamp l2a or |219 respectively.

This clamp is an oblong metal strip of phosphor bronze, No. B. 8a S. gauge for example, divided along its center line for about two-thirds of its length by a slot I3, wide enough to tightly fit over either of the plug-in prongs I4 of the electric plug l5 (Fig. 2). The two legs l2 and 5 I2 are of unequal length, and when the clamps are arranged side by side, as shown in Fig. 3, soldered to the wires IIa and IIb, the two longer legs I2 are on the inside.

These two terminal clamp plates |2a, |2b are framed within and xedly held in place by a nonconductive plate I6, made of hard rubber and about the same thickness as the terminal plates,- in this case about 3%. This plate is shown separately in Fig. 5. It is provided with two longitudinal slots Il starting from the top in a parallel direction, and cut in such a way as to envelop the outer contour of the terminal plate clamps, each starting with a narrow slot I'Ia, inV

which the wires I|a and Hb, respectively, are lorectangular cut-out Hb, which follows the exact outer contour of the clamp plate, except that aside of the shorter legs of the clamps a narrow eXtra clearance IIc is provided in such a way that the 25 cut-outs I'Ib` are a little wider that the clamp. plates |2a or |217. The object of this is that when for instance a tight-fitting prong I4 of the 'plug I5 is pushed into the slot I3 (Fig. 6), the short leg |2" can yield a little sideways to let the prong pass, whereafter it will close tightly upon the side of the prong, insuring a good electrical contact. It is to be noted that the long legs I2 are both held rigidly in place as well as the upper and outer corners |2c` by the little projections I 7d. The lower part of plate I6 is semi-circular and the top part rectangular.

This plate I6 is sandwiched between two other non-conductive plates I8 and |9 which are of the same material, size, thickness and outer contour as plate i6, but are not slotted in the same way. Alike to each other, they both are perforated by a pair of narrow slots 2U and 2| (Fig. 1). These slots, arranged symmetrically to the center line 'of the plates are placed at such a distance from each other that the prongs of a standard plug (about 1/2 center to center) will just fit into them. They also t the cross-section of the prongs (about 1/4 X 1-16) and moreover, when the third plate I6 is sandwiched in between the 50 plates I8 and I9 and an electrical standard plug is inserted through these slots 2D, 2|, the prongs will pass through the slots I3 of the terminals I 2a, b, making electrical contact with both of them, as can be seen from a contemplation o 55 Fig. 3. The three plates I 6, I8 and I9 form a mounting plateV 26 and in order to more rmly support and protect the condenser Ill on top of the three adjacent plates I8, I6, I9, a ferrule v22 is slipped 60 over the entire length of the condenser as well as the top edges of the plates. This ferrule is preferredly made of sheet tin and bent from a symmetrically formed blank in such a way that a cross section resembles the shape shown in 60 Figs. 2 and 4. It win be seen that while. the main portion forms a cylindrical body 22a., the rear end 22C (which otherwise is cut and sweeped along its eXtreme edge alike to the front end, 70 shown in Fig. 1) is joining the cylindrical body at a tangent, while the front end 22h is sharply bent downward so as to form a pair of parallel wings with the rear end to embrace the top edges of the three hard rubber plates between them.

'-75 All three plates as well as the wings 22h, c are then riveted tightly together by means of three eyelet rivets 23. The empty space between the condenser IIJ, the ferrule 22 and the top of the hard rubber plates is nally cast out with asphalt 25 or wax, or some other non-conductive substance.

It is, however, also feasible to form the nonconductive support for the xed condenser out of two pieces only,-instead of three single hard rubber blades, as described; likewise it is possible to use other non-conductive material, for example, a phenol-concentrate, usually called by the trade name: Bakelite, instead of hard rubber.

If for instance the intermediate blade I6 were made integral with either one of the Aouter covers, e. g. plate I9, the slots |'I could be molded simply as recesses on the inner surface of such a plate, while the apertures 20, 2| would be the only openings going through. The front cover I8 would remain as shown in Fig. 1, and both plates forming a sort of pocket could be molded out of Bakelite. The rear plate seen from the inside would have the same appearance as shown in Fig. 3. This modification therefore would likewise come within the legitimate scope of my claims.

Another possibility would be to mold the two plates |2a, b, with the lead-in wires Ila, IIb attached, directly into the interior of a non-Conductive plate, so that when finished, the washerlike support of the condenser would consist of a single integral piece.

If in this case the clamps IZa, b, were simply split in the middle instead of having a wider slot 3 as shown, while the mold had slots cored therein, such as 20, 2| (Fig. 1), the necessary resiliency and electrical contact for the terminals could be secured by swaging or reaming out the slots in the metal plates in such a way that these slots would be a triile narrower than the slots in the molds.

It is thus seen that all the objects of the invention can be attained in a simple, economical and efficient way. The plug I5 may be inserted -into its socket without requiring more additional space than just the combined thickness of the three hard rubber plates, i. e. not more than the thickness of a gse washer. The condenser is kept out of the way, placed either above or below the plug, or to one side, as conditions may demand. It is entirely inconspicuous when installed and constitutes a simple, inexpensive and extremely efcient contrivance which, among other advantages, eliminates all man-made interference during reception.

Many modifications of the construction, as described are feasible without departing from the rspirit of the invention, and the scope of the patent protection sought for should be judged not from the details illustrated but from the claims as hereinafter worded.

Having described my invention, what I claim and desire to protect by Letters Patent, is:-

1. An interference eliminator of the class described comprising a thin, at mounting plate,

a condenser mounted on and supported by said plate, apertures in said plate through which the prongs of a standard attachment plug may be passed to enter a standard outlet socket, said apertures so as to be contacted by the prongs of the plug, and electrical conducting means connecting said terminals to said condenser.

2. An interference eliminator of the class described, comprising a thin, at mounting plate, said plate being of laminated construction and having an intermediate member and a pair of cover members, a condenser adjacent one edge of and supported by the mounting plate, apertures in said mounting plate through which the prongs of a standard attachment plug may be passed to enter a standard outlet socket, said apertures being spaced a sufficient distance from said condenser to permit the insertion of the prongs without the condenser being overlapped by the body of the plug, terminal means for the condenser carried by said intermediate member and enclosed by said cover members, said terminal means being adjacent said apertures so as to be contacted by the prongs of the plug, and electrical conducting means also enclosed by said cover plates for connecting said terminals of said condenser.

3. An interference eliminator of the class described, comprising a thin, flat mounting plate of approm'mately semi-circular shape, a cylindrical condenser attached tangentially to the straight edge of said mounting plate so as to overhang the front surface of said plate, apertures in said plate through which the prongs of a standard attachment plug may be passed to enter a.standard outlet socket, said apertures being spaced a sucient distance from said condenser to permit the insertion of the prongs Without the condenser being overlapped by the body of the plug, terminal means for the condenser carried by said plate and adjacent said apertures so as to be contacted by the prongs of the plug, and electrical conducting means connecting said terminals to said condenser.

4. An interference eliminator of the class described, comprising a thin, flat mounting plate, said plate being of laminated construction and having an intermediate member and a pair of cover members, a condenser adjacent one edge of and supported by the mounting plate, apertures in said mounting plate through which the prongs of a standard attachment plug may be passed to enter a standard outlet socket, said apertures being spaced a suicient distance from said condenser to permit the insertion of the prongs Without the condenser being overlapped by the body of the plug, said intermediate member of the plate having slots in which are received and held terminals for the condenser in such position as to be adjacent said apertures so that the terminals will be contacted by the prongs of the plug, and electrical conducting means also received in the slots of said intermediate member and connecting said terminals to said condenser.

5. An interference eliminator of the class described comprising a thin, flat mounting plate of approximately semi-circular shape, a cylindrical condenser attached tangentially to the Astraight edge of said mounting plate so as to overhang the front surface of said plate, apertures in said plate through which the prongs of a standard attachment plug may be passed to enter a standard outlet socket, said apertures being spaced a suicient distance from said condenser to permit the insertion of the prongs Without the condenser being overlapped by the body of the plug, terminal means for the condenser carried by said plate and adjacent said apertures so as to be contacted by the prongs of the plug, electrical conducting means connecting said terminals to said condenser and a substantially cylindrical ferrule, split lengthwise and provided with extended flanges and slipped over the condenser and mounting plate, and secured to the latter.

6. The combination of claim 4 in which the terminals of the condenser are resilient clamps tting over the prongs of the plug, but capable of yielding so as to spread laterally as the prongs are forced through them.

WILLIAM M. ROBINSON. 

